[Dr. Sivana]

Fresca?

Aspartame, I am afraid. The fountain version may also have saccharin.

Mexican Fresca is sugar (and calorie laden). If you do not need a sugar free version, Squirt can be a substitute.

If you want a zero sugar version that doesn't cost a mint (Zevia), Shasta Zero Sugar Grapefruit is sucralose based.

https://www.shastapop.com/flavors/zero-sugar-grapefruit/

Shasta is cheap, and has an extremely broad range of flavors. It is also tricky to find. Here I can get it at Winco.

As a lad, I enjoyed the full-sugar Canada Dry Wink grapefruit soda. It used to be a flagship product for good ol' Canada Dry (along side the ginger ale). Canada Dry used to have an exceptional Cola called "Jamaica Cola" as well. Went great with ham sandwiches. That one is not coming back. Wink might still exist somewhere.

[Red Badger]

Fresca is a grapefruit flavored drink. Not good with some blood pressure meds...............